For about 10 percent of electricity in the United States, it’s fuel from dismantled nuclear bombs, including Russian ones.

“It’s a great, easy source” of fuel, said Marina V. Alekseyenkova, an analyst at Renaissance Capital and an expert in the Russian nuclear industry that has profited from the arrangement since the end of the cold war.

But if more diluted weapons-grade uranium isn’t secured soon, the pipeline could run dry, with ramifications for consumers, as well as some American utilities and their Russian suppliers.

Already nervous about a supply gap, utilities operating America’s 104 nuclear reactors are paying as much attention to President Obama’s efforts to conclude a new arms treaty as the Nobel Peace Prize committee did.

In the last two decades, nuclear disarmament has become an integral part of the electricity industry, little known to most Americans.

Salvaged bomb material now generates about 10 percent of electricity in the United States — by comparison, hydropower generates about 6 percent and solar, biomass, wind and geothermal together account for 3 percent.

Utilities have been loath to publicize the Russian bomb supply line for fear of spooking consumers: the fuel from missiles that may have once been aimed at your home may now be lighting it.

But at times, recycled Soviet bomb cores have made up the majority of the American market for low-enriched uranium fuel. Today, former bomb material from Russia accounts for 45 percent of the fuel in American nuclear reactors, while another 5 percent comes from American bombs, according to the Nuclear Energy Institute, an industry trade association in Washington.

Treaties at the end of the cold war led to the decommissioning of thousands of warheads. Their energy-rich cores are converted into civilian reactor fuel.

In the United States, the agreements are portrayed as nonproliferation treaties — intended to prevent loose nukes in Russia.

In Russia, where the government argues that fissile materials are impenetrably secure already, the arms agreements are portrayed as a way to make it harder for the United States to reverse disarmament.

The program for dismantling and diluting the fuel cores of decommissioned Russian warheads — known informally as Megatons to Megawatts — is set to expire in 2013, just as the industry is trying to sell it forcefully as an alternative to coal-powered energy plants, which emit greenhouse gases.

Finding a substitute is a concern for utilities today because nuclear plants buy fuel three to five years in advance.

One potential new source is warheads that would become superfluous if the United States and Russia agree to new cuts under negotiations to renew the Strategic Arms Reduction Treaty, which expires on Dec. 5.

Such negotiations revolve around the number of deployed weapons and delivery vehicles. There is no requirement in the treaty that bomb cores be destroyed. That is negotiated separately.

For the industry, that means that now, as in the past, there will be no direct correlation between the number of warheads decommissioned and the quantity of highly enriched uranium or plutonium, also used in weapons, that the two countries declare surplus.

(This summer, Mr. Obama and President Dmitri A. Medvedev of Russia agreed to a new limit on delivery vehicles of 500 to 1,100 and a limit on deployed warheads as low as 1,500. The United States now has about 2,200 nuclear warheads and the Russians 2,800.)

Mr. Medvedev has reaffirmed Russia’s commitment to a 2000 agreement to dispose of plutonium, and both countries plan to convert that into reactor fuel as well.

An American diplomat and an official with a federal nuclear agency in Washington have confirmed, separately, that the two countries are quietly negotiating another agreement to continue diluting Russia’s highly enriched uranium after the expiration of Megatons to Megawatts, using some or all of the material from warheads likely to be taken out of the arsenals.

The government officials were not authorized to publicly discuss these efforts.

This possible successor deal to Megatons to Megawatts is known in the industry as HEU-2, for a High Enriched Uranium-2, and companies are rooting for it, according to Jeff Combs, president and owner of Ux Consulting, a company tracking uranium fuel pricing.

“You can look at it like a couple of very large uranium mines,” he said of the fissile material that would result from the program.

American reactors would not shut down without a deal; utilities could turn to commercial imports, which would most likely be much more expensive.

To make fuel for electricity-generating reactors, uranium is enriched to less than 5 percent of the isotope U-235. To make weapons, it is enriched to about 90 percent U-235.

The United States Enrichment Corporation, a private company spun off from the Department of Energy in the 1990s, is the treaty-designated agent on the Russian imports. It, in turn, sells the fuel to utilities at prevailing market prices, an arrangement that at times has angered the Russians.

Since Megatons to Megawatts has existed, American utilities operating nuclear power plants, like Pacific Gas & Electric or Constellation Energy, have benefited as the abundance of fuel that came onto the market drastically reduced overall prices and created savings that were ultimately passed along to consumers and shareholders.

Nuclear industry giants like Areva, the French company; the United States Enrichment Corporation and Nuclear Fuel Services, another American company; and Rosatom, the Russian state nuclear corporation, are deeply involved in recycling weapons material and will need new supplies to continue that side of their businesses.

In the United States, domestic weapons recycling programs are smaller in scale and would be no replacement for Megatons for Megawatts. The Nuclear Fuel Services, in Erwin, Tenn., in 2005 began diluting uranium from the 217 tons the government declared surplus; so far 125 tons have been processed. It is used at the Tennessee Valley Authority plant.

The American plutonium recycling program is also well under way at a factory being built at the Energy Department’s Savannah River site in South Carolina to dismantle warheads from the American arsenal; a type of plutonium fuel, called mixed-oxide fuel, will come on the market in 2017.

In total, the 34 tons to be recycled there are expected to generate enough electricity for a million American homes for 50 years.

This article has been revised to reflect the following correction:

Correction: November 11, 2009
A subheading on Tuesday with an article about the use of old nuclear bomb cores to produce electricity misstated the source of the bomb material used to generate power in the United States. It comes from bombs dismantled by both the United States and Russia — not from Russian bombs alone.